Problem: Solve for $n$ : $-30 = n - 17$
Solution: Add $17$ to both sides: $ \begin{eqnarray} \\ \hphantom{-30 {+ 17}} &\hphantom{=}& \hphantom{n} \\ -30 &=& n - 17 \\ \\ {+17} && {+17} \\ \end{eqnarray} $ $ \begin{eqnarray} \\ -30 {+ 17} &=& n \\ \end{eqnarray} $ Simplify. $ n = -13$